An improved heuristic for minimizing makespan among m identical parallel processors

A simple heuristic for minimizing makespan among identical processors assigned independent tasks is presented and explored. The heuristic initially assigns jobs to processors by applying a quick and effective algorithm which at present is commonly applied to this problem. The heuristic then seeks to identify pairs of jobs that may be interchanged between processors to improve the solution. The conditions under which an optimal makespan may be achieved by such an interchange are derived for the case of two processors. The procedure is then extended to three or more processors. Results of 700 randomly generated problems are reported. The heuristic achieved an optimal solution for most of the problems. The worst case performance for the heuristic has not been established; however, evidence is presented that the worst case for the heuristic is considerably smaller than that of algorithms presently used.     

Debate over relevance.

Argues that there may be more to the debate over relevance in psychology than implied by J. Baron (see record 1972-10028-001). E. Walker (see record 1971-07202-001) cautioned against being too superficial or delving too deep in the search for relevance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parametric analysis of brain stimulation reward in the rat: III. Effect of performance variables on the reward summation function.

Defines the reward summation function as the empirical function relating running speed in a runway and waiting-box paradigm to the number of electrical pulses a rat receives for running. 5 experiments with male white rats are described in which repeated determination of this function was made, with other performance variables-priming, task difficulty, degree of training, health, and pharmacological state of the rat-varied between determinations. Results show that these other performance factors affected the height (asymptotic speed) of the function but not the location of the sharp rise in the function. It is concluded that since manipulation of stimulation parameters that affect the amount of reward excitation substantially alters the location of the sharp rise, the reward summation function provides a suitable basis for a neuropharmacological investigation of the reward effect in self-stimulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Biomechanical Evaluation of Two Methods of Manual Load Lifting

Since the middle 1930's it has been advocated that all lifting should be carried out with the back near vertical and with the knees bent. The basis for this recommendation has been that it shifts the stresses on the body from the low-back to the legs. Under certain conditions this recommendation is invalid. In this paper Chaffin and Baker's biomechanical lifting model is extended by considering the erector spinae muscles and by considering load accelerations. Mathematical modeling shows that forces on the erector spinae muscles and the lumbosacral disc can be as much as 50% higher when using the recommended “straight back, bent knees” method when compared to the common “stooped back” method. The straight back method is recommended only for lifts when the object is initially close to the spine.     

Thermal characterization of PMMA-based bone cement curing

In thermal characterization tests of polymethylmethacrylate bone cement performed according to the ASTM Standard Specification for Acrylic Bone Cement, time-temperature profiles of bone cement were observed to be sensitive to the thickness of the cement patty and the mold material. Due to the heat transfer from cement to the surrounding mold, such tests might underestimate the exothermic temperature of bone cement. Developing test methods to better characterize cement thermal behavior is necessary for accurate cement curing simulations. In this paper, the effects of the mold material and geometry on experimental measurements of bone cement setting temperature and setting time were evaluated by conducting the polymerization in different test molds. Finite element (FE) numerical simulations were also performed to provide a further understanding of these effects. It was found that the mold material and geometry significantly influence the values of the parameters measured using the ASTM standard. Results showed that the setting temperature measured was about 50 degrees C lower in a polytetrafluoroethylene (PTFE) mold than in a polyurethane (PU) foam mold for the 6 mm thickness cement. The measured peak temperature using PTFE molds varied about 75 degrees C for different mold heights (6mm vs. 40 mm), but only by 28 degrees C with PU molds. The measured setting time with PTFE molds varied by about 740 s for different mold heights (6 mm vs. 40 mm), while only by about 130 s for PU molds. Using PU foam materials for the test mold decreases cement heat transfer effects due to the poor heat conductivity of PU foam and provides more consistent measured results. FE parametric studies also support these observations. Poor conductivity materials, like PU foam, make better molds for the characterization of bone cement thermal behavior.     

Short-run maquiladora employment dynamics in Tijuana

The Tijuana maquiladora sector has grown enormously over the past two decades. Short-term time series characteristics of this segment of the regional economy are analyzed in an attempt to clarify labor market behavior associated with this remarkable performance. Parameter estimation is accomplished using linear transfer function analysis. Data are drawn from the January 1980–December 2000 sample period. Empirical results indicate that real wage rates, maquiladora plants, United States industrial activity, and the real exchange rate of the peso play significant roles in determining month-to-month fluctuations in maquiladora employment. Sub-sample simulation exercises are conducted using a random walk benchmark in order to examine forecast accuracy. Empirical results indicate that the linear transfer function technique provides relatively accurate forecasts all step-lengths.Helpful comments were provided by Tschangho John Kim, Tim Roth, Richard Posthuma, Henry Herzog, Mohammed Mohsin, and two anonymous referees. Partial financial support was provided by El Paso Electric Company, City of El Paso Office of Economic Development, and Wells Fargo Bank of El Paso.Views expressed in this study are strictly those of the authors and do not necessarily reflect the positions of the Federal Reserve Bank of Dallas or of the Federal Reserve System.Received: October 2002/Accepted: October 2003     

Applications of contaminant fate and bioaccumulation models in assessing ecological risks of chemicals: a case study for gasoline hydrocarbons

Mass balance models of chemical fate and transport can be applied in ecological risk assessments for quantitative estimation of concentrations in air, water, soil, and sediment. These concentrations can, in turn, be used to estimate organism exposures and ultimately internal tissue concentrations that can be compared to mode-of-action-based critical body residues that induce toxic effects. From this comparison, risks to the exposed organism can be evaluated. To demonstrate the use of fate models in ecological risk assessment, we combine the EQuilibrium Criterion (EQC) environmental fate model with a simple screening level biouptake model for three representative organisms: a bird, a mammal, and a fish. This effort yields estimates of internal body concentrations that can be compared with levels known to elicit toxic effects. As an illustration, we present an analysis of 24 hydrocarbon components of gasoline that differ in properties but are assumed to elicit toxicity by a common narcotic mode of action. Results demonstrate that differences in chemical properties and mode of entry into the environment lead to profound differences in the efficiency of transport from emission to target biota. We discussthe implications of these results and draw attention to the insights gained about regional fate and ecological risks associated with gasoline. This approach is suitable for assessing single chemicals or mixtures that have similar modes of action. We conclude that the model-based methodologies presented are widely applicable for screening level ecological risk assessments that support effective chemicals management.     

DNA mutation detection in a polymer microfluidic network using temperature gradient gel electrophoresis

A miniaturized system for DNA mutation analysis, utilizing temperature gradient gel electrophoresis (TGGE) in a polycarbonate (PC) microfluidic device, is reported. TGGE reveals the presence of sequence heterogeneity in a given heteroduplex sample by introducing a thermal denaturing gradient that results in differences between the average electrophoretic mobilities of DNA sequence variants. Bulk heater assemblies are designed and employed to externally generate temperature gradients in spatial and temporal formats along the separation channels. TGGE analyses of model mutant DNA fragments, each containing a single base substitution, are achieved using both single- and 10-channel parallel measurements in a microfluidic platform. Additionally, a comprehensive polymer microfluidic device containing an integrated microheater and sensor array is developed and demonstrated for performing spatial TGGE for DNA mutation analysis. The device consists of two PC modular substrates mechanically bonded together. One substrate is embossed with microchannels, and the other contains a tapered microheater, lithographically patterned along with an array of temperature sensors. Compared with the external heating approaches, the integrated platform provides significant reduction in power requirement and thermal response time while establishing more accurate and highly effective control of the temperature gradient for achieving improved separation resolution.     

Aurora: a new model and architecture for data stream management

This paper describes the basic processing model and architecture of Aurora, a new system to manage data streams for monitoring applications. Monitoring applications differ substantially from conventional business data processing. The fact that a software system must process and react to continual inputs from many sources (e.g., sensors) rather than from human operators requires one to rethink the fundamental architecture of a DBMS for this application area. In this paper, we present Aurora, a new DBMS currently under construction at Brandeis University, Brown University, and M.I.T. We first provide an overview of the basic Aurora model and architecture and then describe in detail a stream-oriented set of operators.Received: 12 September 2002, Accepted: 26 March 2003, Published online: 21 July 2003Edited by Y. Ioannidis